1. Field of the Invention
This invention relates to a ventilation system for efficiently removing cooking effluents and combustion products from the exhaust of a cooking appliance.
2. Description of Related Art
Traditionally, restaurant kitchens are ventilated by capturing the cooking effluents and, in the case of gas-fired appliances, combustion products in a hood and transporting the grease-laden exhaust airflow from the inside of the building to the outdoors through welded steel ducts. The grease load in the welded steel ducts is reduced by fitting the hoods with a baffler or slot filters that remove the heavier grease particles by impaction. The smaller, lighter grease particles and grease vapors bypass these filters and deposit on the duct walls and the building creating fire and safety issues.
Traditional kitchen ventilation systems are expensive, in no small part because of the welded steel ductwork, resulting in acceptance of recirculating ventilation technology that does not require the removal of all exhaust airflow from the building. Such recirculating ventilation technology typically includes a hood and a grease filtering element to capture grease from the cooking effluents and combustion products from the gas-fired appliance. An odor removal or control element is also positioned within the hood together with a blower to return the scrubbed air back to the interior of the building. A fire suppression device is also required to control the dangers associated with ignition of grease or other combustion products.
The grease filtering element according to related art devices may comprise an electronic air cleaner such as an electrostatic precipitator (ESP) or HEPA filters. Such electronic air cleaners are often used to filter air drawn into the building and more recently are used to clean grease-laden exhaust airflow prior to recirculation back into the building. These systems must have fire suppression devices because the electronic air cleaners use a high field voltage and may act as an ignition source. Further, grease may collect within the device and may ignite if a fire starts in an appliance positioned beneath the device.
Several existing recirculation ventilation units featuring ESP technology followed by charcoal granular filters are now in use. In such devices, the ESP modules are largely effective only in removing grease particles and droplets with little impact on grease vapor and cooking odors. However, grease vapor may account for approximately 50-60% by weight of the grease emitted during frying and approximately 40% by weight of the grease emitted during char-broiling. Given the apparent lack of effectiveness of the ESP modules in removing grease vapor, the charcoal filters located upstream become coated with grease vapor and are thus only marginally effective with respect to their primary function, odor control. Finally, the ESP modules must be maintained on a regular, often times daily basis to clean grease from internal plates or the performance of the ESP modules quickly drops off.
Therefore, there exists a need for a low cost, low maintenance ventilation system that will effectively remove cooking effluents and combustion products, as well as associated odors, from the exhaust of a cooking appliance.